This invention refers to a composition for waving of human hair, i.e. a permanent waving composition, providing an excellent waving effect, particularly leading to a uniform permanent wave with elastic curls and good combability, avoiding damage of the hair texture, also when applied repeatedly, but rather causing a conditioning effect and producing expressive lustre on the hair.
It is well-known that permanent waving is performed in a two-step process, i.e., reductive splitting of cystine disulfide bonds of the hair by the action of a reducing agent and subsequent neutralization or fixing of the wave by the application of an oxidizing agent whereby the cystine disulfide bonds are restored.
The reducing agent most commonly used is still thioglycolic acid, particularly the ammonium salt, although numerous other thio compounds have been suggested for this purpose which, however, have not been generally accepted in practical use.
The compositions comprising thioglycollate are normally used at a pH-value between 8 and 10, particularly from 8.5 to 9.5, which may cause hair damage when repeatedly applied within short intervals.
There have been attempts to circumvent these disadvantages by the creation of so-called "acidic permanent waving solutions" with a pH-value in the range from 6.8 to 7.8, i.e. near neutral. The reducing agent most frequently employed for this purpose is thioglycolic acid monoglycerol ester. However, this material has proved to have a skin irritating and sensitizing potential on some users, so that this solution of the problem is not optimal either.